Effects of dietary zinc source on the metabolic and immunological response to lipopolysaccharide in lactating Holstein dairy cows

The objectives of this study were to evaluate the effects of replacing 40 mg/kg of Zn from Zn sulfate (control; CON) with Zn AA complex (AvZn) on metabolism and immunological responses following an intravenous lipopolysaccharide (LPS) challenge in lactating cows. Cows were randomly assigned to 1 of 4 treatments: (1) pair-fed (PF) control (PF-CON; 5 mL of saline; n = 5), (2) PF AvZn (PF-AvZn; 5 mL of saline; n = 5), (3) LPS euglycemic clamp control (LPS-CON; 0.375 μg of LPS/kg of BW; n = 5), and (4) LPS euglycemic clamp AvZn (LPS-AvZn; 0.375 μg of LPS/kg of BW; n = 5). Cows were enrolled in 3 experimental periods (P). During period 1 (3 d), cows received their respective dietary treatments and baseline data were obtained. During period 2 (P2; 2 d), a 12-h LPS euglycemic clamp was conducted or cows were PF to their respective dietary counterparts. During period 3 (P3; 3 d), cows received their dietary treatment and consumed feed ad libitum. Mild hyperthermia (1°C) was observed in LPS cows at 3 h postbolus. Throughout P2, the rectal temperature of LPS-AvZn cows was decreased (0.3°C) relative to LPS-CON cows. Administrating LPS decreased dry matter intake (47%) during P2, and by experimental design the pattern was similar in PF cohorts. During P3, dry matter intake from LPS cows remained decreased (15%) relative to PF cows. Milk yield from LPS cows decreased (54%) during P2 relative to PF cows, but it was similar during P3. During P2, somatic cell count increased 3-fold in LPS cows relative to PF controls. Dietary AvZn tended to decrease somatic cell count (70%) during P3 relative to LPS-CON cows. Insulin increased 7-fold in LPS cows at 12 h postbolus and remained increased (4-fold) for the duration of P2. Circulating glucagon from LPS cows increased (65%) during P2, and supplementing AvZn blunted the increase (30% relative to LPS-CON). During P2, circulating cortisol increased 7-fold post-LPS infusion relative to PF cows, and supplementing AvZn decreased cortisol (58%) from 6 to 48 h postbolus relative to LPS-CON cows. Administrating LPS increased circulating LPS-binding protein and serum amyloid A (3- and 9-fold, respectively) relative to PF cows. Compared with LPS-CON, LPS-AvZn cows had increased circulating serum amyloid A (38%) 24 h postbolus. The 12-h total glucose deficit was 36 and 1,606 g for the PF and LPS treatments, respectively, but was not influenced by Zn source. In summary, replacing a portion of the Zn sulfate with Zn AA complex appeared to reduce the inflammatory response but had no effect on the glucose deficit.     

Effects of level and form of dietary zinc on dairy cow performance and health

A basal mixed ration supplying 36 mg of Zn/kg of dry matter (DM) was supplemented with 1 of 4 concentrates differing in level and form of dietary Zn. The concentrates were fed at 2 kg/cow per day and contained 300 mg of Zn/kg (to supply the total recommended level, according to NRC (2001); R) or 60 mg of Zn/kg (to supply 0.66 of the total recommended level; L), either supplemented as ZnO (I) or organically chelated Zn (O). Forty-four Holstein-Friesian dairy cows (12 primiparous and 32 multiparous), on average 31 d (SD ± 11.4) into lactation, were allocated to 1 of the 4 treatments. All cows remained on the treatment for 14 wk. The data was analyzed by ANOVA as a 2 × 2 factorial design. Dry matter intake averaged 23.5 kg/d and did not differ between treatments. Cows supplemented with organically chelated Zn at the recommended level of inclusion (RO) had a higher milk yield (37.6 kg/d) than those fed inorganic Zn at the recommended level (RI; 35.2 kg/d) or organically chelated Zn at the low level (LO; 35.2 kg/d), but was not different from those fed inorganic Zn at the low level (LI; 36.0 kg/d). Milk composition was unaffected by dietary treatment. Animals that received the low level of Zn (LI and LO) had higher somatic cell counts [3.97 and 3.93 versus 4.35 and 4.55 (log_e) for RI, RO, LI, and LO, respectively] and milk amyloid A levels than those receiving the recommended levels (RO and RI). There was no effect of treatment on body condition score, body weight, or locomotion score. Hoof hardness improved over the duration of the study but there were no differences between treatments. Similarly, blood plasma mineral levels for Zn, Cu, Mo, and Fe were not affected by treatment, whereas there was a trend for increased ceruloplasmin levels in cows receiving the recommended compared with the low level of Zn, but there was no effect of mineral form. There was also no effect of treatment on superoxide dismutase activity or blood hematology. It is concluded that supplementing Zn at the recommended level reduced somatic cell counts and milk amyloid A levels, whereas supplementation in an organic form at the recommended level also increased milk yield.     

Associations of somatic cell count with milk yield and reproductive performance in grazing dairy cows

Poor udder health status can have a detrimental effect on milk yield and reproductive performance, leading to reductions in the dairy farm profit. The objective of this retrospective longitudinal study was to assess the associations of somatic cell count (SCC) with daily milk yield and reproductive performance. A database with 1,930,376 lactations from 867 Argentinean grazing dairy herds records collected for 14 years was used. The association of the evolution of SCC (healthy vs. new case vs. cured vs. chronic; with 150,000 SCC/mL as threshold) and of the severity of SCC [mild (150,000­–400,000 SCC/mL) vs. moderate (400,000–1,000,000 SCC/mL) vs. severe (>1,000,000 SCC/mL)] with the odds for conception were estimated. Finally, the associations of the linear score of SCC (LS-SCC) with daily milk yield were estimated depending on parity and milk production quartile. The odds ratios (CI 95%) for conception at first service were 0.921 (0.902–0.941), 0.866 (0.848–0.884), and 0.842 (0.826–0.859) for the new case, cured, and chronic cows compared with healthy cows, respectively. Also, the odds ratios (CI 95%) for conception were 0.902 (0.881–0.925), 0.837 (0.808–0.866) and 0.709 (0.683–0.736) for mild, moderate and severe cases compared with healthy cows, respectively. An increase of one point of LS-SCC was associated with decreases of 0.349, 0.539, and 0.676 kg in daily milk yield for first-, second-, and third-lactation cows, respectively. In conclusion, SCC is negatively associated with the risk for conception and with daily milk yield in grazing dairy cows. This negative relationship with conception is higher when SCC increase occurs after the service date and it is influenced by severity of mastitis, and in the case of milk yield, the negative association is influenced by parity, milk production quartile, and severity of mastitis.     

Production performance of Holstein cows at 4 stages of lactation fed 4 dietary crude protein concentrations

Dairy cow responses to dietary crude protein (CP) may depend on stage of lactation. The primary objective of this study was to evaluate the effects of 4 concentrations of dietary CP on dry matter intake (DMI), production performance, net energy for lactation (NE_L) output in milk, feed efficiency (FE: milk NE_L/DMI), and nitrogen use efficiency (100 × milk protein-N/N intake) when fed to cows grouped as early, mid-early, mid-late, and late lactation. Our secondary objective was to determine the range of CP concentration at which production responses were not negatively affected across days in milk (DIM). Multiparous Holstein cows (n = 64) were stratified by DIM [initial average ± standard deviation: 86 ± 14.9 (early), 119 ± 10.0 (mid-early), 167 ± 22.2 (mid-late), and 239 ± 11.1 (late)] and then randomly assigned within DIM group to receive 1 of 4 total mixed rations containing 13.6, 15.2, 16.7, and 18.3% CP (dry matter basis) according to a 4 × 4 factorial arrangement of treatments. Cows were individually fed a covariate diet for 14 d, followed by 56 d of treatment diets. Milk yield and DMI were recorded daily and milk components were analyzed weekly for 2 consecutive days at 3 daily milkings. Data were analyzed using a categorical mixed-effect model to evaluate the effects of CP concentration and DIM using linear, quadratic, and cubic contrasts, and their interactions. Additionally, a mixed-effect cubic regression model was fit with DIM, dietary CP concentration, and their interaction as continuous independent variables. Dietary CP concentration deemed optimal across DIM was determined as the range of CP for which the dependent responses did not differ from the predicted maximum. With advancing stage of lactation, DMI, milk NE_L output, and FE decreased linearly (from 30.4 to 28.4 kg/d for DMI, from 33.2 to 23.3 Mcal/d for NE_L output, and from 1.09 to 0.82 Mcal milk NE_L/kg DMI for FE for early and late lactation cows, respectively). Responses to dietary CP concentration were linear, quadratic, and cubic with the greatest values observed when cows were fed the 16.7% CP diet across DIM (30.8 kg/d, 31.0 Mcal/d, and 1.01 Mcal/kg for DMI, milk NE_L output, and FE, respectively). There was an interaction between dietary CP concentration and stage of lactation for DMI, milk NE_L output, milk component yield, and FE, which was due to the decline in response to additional CP as lactation progressed. Compared with the 16.7% CP diet, feeding the 18.3% CP diet decreased milk NE_L 0.81 and 5.3 Mcal/d for early and late lactation cows, respectively, indicating that feeding a higher CP concentration in late lactation had a negative effect on cow performance. Nitrogen use efficiency declined linearly with increasing CP concentration and DIM. Regression analysis suggested that dietary CP ranging from 16.3 to 17.4% maintained production in early and mid-early lactation. However, dietary CP could be reduced to between 15.7 and 17.1% in late lactation. This research suggested that there are distinct ranges of dietary CP concentrations that maintain cow performance at each stage of lactation.     

Genetic and environmental parameters for milk production, udder health, and fertility traits in Mexican Holstein cows

Genetic and phenotypic parameters for Mexican Holstein cows were estimated for first- to third-parity cows with records from 1998 to 2003 (n = 2,971-15,927) for 305-d mature equivalent milk production (MEM), fat production (MEF), and protein production (MEP), somatic cell score (SCS), subsequent calving interval (CAI), and age at first calving (AFC). Genetic parameters were obtained by average information matrix-REML methodology using 6-trait (first-parity data) and 5-trait (second- and third-parity data) animal models. Heritability estimates for production traits were between 0.17 ± 0.02 and 0.23 ± 0.02 for first- and second-parity cows and between 0.12 ± 0.03 and 0.13 ± 0.03 for third-parity cows. Heritability estimates for SCS were similar for all parities (0.10 ± 0.02 to 0.11 ± 0.03). For CAI, estimates of heritability were 0.01 ± 0.05 for third-parity cows and 0.02 ± 0.02 for second-parity cows. The heritability for AFC was moderate (0.28 ± 0.03). No unfavorable estimates of correlations were found among MEM, MEF, MEP, CAI, and SCS. Estimates of environmental and phenotypic correlations were large and positive among production traits; favorable between SCS and CAI; slightly favorable between MEM, MEF, and MEP and SCS, between AFC and SCS, and between SCS and CAI; and small but unfavorable between production traits and CAI. Estimates of genetic variation and heritability indicate that selection would result in genetic improvement of production traits, AFC, and SCS. Estimates of both heritability and genetic variation for CAI were small, which indicates that genetic improvement would be difficult.     

Effect of zinc source and dietary level on zinc metabolism in Holstein calves

Forty-eight Holstein male calves were stratified by origin and body weight and randomly assigned to one of 4 treatment groups. Dietary treatments were administered in 2 phases. In phase 1, treatment groups received the basal diet with no supplemental Zn (control), basal diet plus 20 mg of Zn/kg of DM as ZnSO4 or Zn proteinate (ZnProt), or basal diet plus 20 mg of Zn/kg of DM with 50% of the Zn supplied from each source (ZnM) for 98 d. In phase 2, calves continued to receive the same Zn source fed in phase 1; however, half of the calves in each treatment group were randomly selected to receive 500 mg of Zn/kg of DM (HiZnSO4, HiZnProt, HiZnM) for 14 d. Gain, feed intake, and feed efficiency of calves were not affected by treatment in either phase of the experiment. Treatment had no affect on plasma Zn concentration or alkaline phosphatase activity in phase 1, but liver Zn concentration was greater in calves fed ZnSO4 than those fed ZnProt. In phase 2, plasma Zn was greater in calves fed HiZnProt and HiZnM than in those fed HiZnSO4. Liver Zn was greater in calves fed HiZnProt than in those fed HiZnSO4. Duodenal Zn concentrations were greater in calves supplemented with HiZnProt and HiZnM than those supplemented with HiZnSO4. Liver metallothionein was greater in calves that received 500 mg of Zn/kg than in calves that received 20 mg of Zn/ kg, but was not affected by Zn source. Calves fed HiZnProt and HiZnM had greater kidney Zn concentrations than those fed HiZnSO4. Heart, spleen, testicular, and bone Zn concentrations were not affected by Zn source. Hoof wall samples contained nearly 3-fold greater Zn concentrations than hoof sole. Calves fed ZnSO4 had greater Zn concentration in hoof wall samples than those fed ZnM. Hoof sole Zn concentration was not affected by Zn source or concentration. Plasma and tissue Zn concentrations at harvest were generally similar in calves supplemented with 20 mg of Zn/kg from ZnSO4 or ZnProt. However, when supplemented at 500 mg of Zn/kg, ZnProt was absorbed to a greater extent than ZnSO4, based on higher plasma, liver, duodenal, and kidney Zn concentrations.     

Administration of bovine somatotropin in early lactation: a meta-analysis of production responses by multiparous Holstein cows

A meta-analysis was conducted to assess production responses before 90 d in milk (DIM) when bovine somatotropin (bST) administration was initiated between 5 and 35 DIM. The database was developed from 13 studies of multiparous cows that were published between 1985 and 2006 and from an unpublished study that complied with the study selection criteria. The database included results from 842 cows and provided 50 treatment means for the effect of bST on 3.5% fat-corrected milk (FCM) in early lactation. Effects of bST were investigated using mixed model procedures that included fixed (intercept and slope) and random (intercept and slope) effects for independent variables. Yields of milk (38.6 ± 1.3 kg/d) and FCM (37.6 ± 1.6 kg/d) by control cows before 90 DIM were increased by 2.6 ± 0.8 and 3.2 ± 0.6 kg/d by bST administration. Fat content in milk from bST-treated cows was 0.31 ± 0.10 percentage units greater than that from control cows (3.46 ± 0.13%) but milk protein content (2.95 ± 0.03%) was not altered by bST. Milk fat (1.39 ± 0.10 kg/d) and protein (1.15 ± 0.04 kg/d) yields by controls were increased 0.16 ± 0.03 and 0.07 ± 0.03 kg/d by bST, respectively. Dry matter intake and body weight loss were not altered by bST before 90 DIM, but duration of negative energy balance was prolonged and overall energy balance during this interval reduced when cows were treated with bST. Results are consistent with the premise that bST-treated cows partition nutrients and energy toward milk synthesis for a longer duration and thus likely need a longer interval to replenish their body reserves than cows not treated with bST. Production responses to bST were not altered when cows consumed typical early-lactation diets supplemented with fat except that supplemental fat tended to decrease the magnitude of the effect of bST on milk fat content and decreased the effect of bST on fat and protein yield. Yield of FCM increased curvilinearly with the amount of bST administered. Results indicate that initiation of bST administration to cows before 35 DIM increased FCM yield but the response was at the low end of that typically observed when bST administration is initiated in wk 9 of lactation.     

Characterizing the metabotype and its persistency in lactating Holstein cows: An approach toward metabolic efficiency measures

The variation in feed efficiency among dairy cows is due to differences in fermentation and digestion characteristics, but recent studies have suggested that various aspects of postabsorptive metabolic processes including heat production or the metabolizable energy for maintenance are more crucial. Thus, metabolic efficiency largely determines feed efficiency, but whether divergent feed efficient cows differ in O₂ consumption and metabolic CO₂ production, directly determining the metabolic rate has not been investigated. Therefore, the objective of the present study was to determine whether variation in ME intake (MEI), O₂ consumption, and metabolic CO₂ production account for the variation in metabolic efficiency of dairy cows and whether this effect persists across the lactation cycle. Eighteen cows with different German breeding value functional herd life were kept in freestalls with ad libitum access to a total mixed ration that was kept constant in composition throughout the first lactation. Cows were blood sampled and weighed at wk 5, 13, and 42 postpartum (pp) and transferred into respiration chambers. Animals were retrospectively clustered according to MEI, O₂ consumption, and metabolic CO₂ production, each normalized to metabolic body weight (mBW). Cluster analysis revealed 9 high metabolically efficient (high-Meff) and 9 low metabolically efficient cows. The high-Meff cows had greater MEI and feed conversion efficiency, produced less metabolic CO₂ and methane, had a stronger negative energy balance, and tended to have a lower metabolic respiratory quotient. Further, high-Meff cows had lower residual MEI, less heat energy loss, and lower plasma glucose concentrations, but used a greater portion of body reserves instead of feed energy for milk synthesis, particularly at wk 5 and 13 pp. However, these group differences did not persist by wk 42 pp. Cow groups were not different in O₂ consumption, milk yield, metabolizable energy for maintenance, or the efficiency of tissue utilization for milk synthesis, but high-Meff cows tended to have the lower German relative breeding value functional herd life, indicating a link between metabolic performance and productive lifespan. In conclusion, the use of a clustering approach involving MEI/mBW, O₂/mBW, and CO₂/mBW seems to be a promising method to differentiate cows with divergent metabolic efficiency but does not allow identifying an individual metabotype that persists across the whole lactation cycle.     

Identification of single nucleotide polymorphisms in the bovine interleukin-12 and interleukin-23 receptor genes and their associations with health and production traits in Holstein cows

Interleukin-12 (IL-12) and interleukin-23 (IL-23) are proinflammatory cytokines produced by macrophages and dendritic cells in response to infection with intracellular pathogens. The IL-12 receptor (IL-12R) is a heterodimer composed of 2 subunits, β1 and β2. The IL-23 receptor (IL-23R) is a heterodimer composed of the IL-12Rβ1 subunit and a unique IL-23R subunit. Given the importance of IL-12 and IL-23 for modulating inflammation and the host immune response, the IL-12 and IL-23 receptor genes may be suitable candidate genes for studying disease resistance in dairy cattle. We hypothesize that single nucleotide polymorphisms (SNP) exist within these genes and that they contribute to variation in health and production traits in dairy cattle. To investigate this, a selective DNA pool was constructed using bull semen based on the estimated breeding values for somatic cell score (SCS), an indicator trait used to achieve genetic improvement for resistance to mastitis. Gene segments were amplified from this pool by PCR and the amplicons were sequenced to reveal SNP. A total of 10 SNP, including 2 in IL-12Rβ1, 5 in IL-12Rβ2, and 3 in IL-23R were identified. The SNP (n = 5) were found in the 5′ untranslated region (UTR) putative promoter regions of the genes, and SNP IL-23R c.1714A > C was a nonsynonymous SNP. Canadian Holstein bulls (n = 492) were genotyped using Sequenom MassARRAY (Sequenom Inc., San Diego, CA). No association was found with SCS based on bull deregressed estimated breeding values for SCS; however, associations of SNP in the IL-12Rβ2 gene (c.-511A > G, c.87A > G, c.2957A > C) were found with milk and protein yield. Further investigation will be required to elucidate the biological and practical relevance of these SNP.     

Comparison of brown midrib sorghum-sudangrass with corn silage on lactational performance and nutrient digestibility in Holstein dairy cows

Total mixed rations containing brown midrib sorghum-sudangrass silage (bmrSS) or corn silage (CS) at either 35 or 45% of dietary dry matter were fed to Holstein dairy cows to determine the effect on lactational performance and nutrient digestibility. Twelve cows were assigned to 1 of 4 diets in replicated 4 × 4 Latin squares with 21-d periods. In vitro 30-h neutral detergent fiber digestion, measured before the start of the trial, was 46.0% for CS and 58.3% for bmrSS. Dry matter intake was greatest when cows were fed the 35% CS (23.4 kg/d) and 45% CS (23.2 kg/d) diets, was least when cows were fed the 45% bmrSS diet (17.6 kg/d), and was intermediate when cows were fed the 35% bmrSS diet (20.1 kg/d). The bmrSS diets resulted in greater body weight gain per 21-d period but similar body condition scores compared with the CS diets. Yield of solids-corrected milk (SCM) was similar among the diets. Efficiency (SCM:dry matter intake) was 28% greater for cows fed the bmrSS than those fed the CS diets. In vivo digestibilities of organic matter and crude protein were greater for the CS diets than the bmrSS diets, but total tract digestibilities of neutral detergent fiber and starch were similar among diets. Ruminal pH was greater when cows were fed the 45% bmrSS diet (6.58), was least when cows were fed the 35% CS (6.10) and 45% CS diets (6.13), and was intermediate when cows were fed the 35% bmrSS diet (6.42). The ratio of acetate to propionate was greater for the bmrSS diets (2.77) than for the CS diets (2.41), with no difference among diets in total volatile fatty acid concentrations (122 mM). In conclusion, cows fed bmrSS had greater efficiency of SCM production, higher ruminal pH, and greater acetate to propionate ratios than cows fed CS. With these diets fed in a short-term study, bmrSS appeared to be an effective alternative to the CS hybrid when fed at either 35 or 45% of dietary dry matter.     

Lactation performance of Holstein cows treated with 2 formulations of recombinant bovine somatotropin in a large commercial dairy herd in Brazil

The objectives of this controlled study were to compare the effects of 2 different formulations of recombinant bovine somatotropin (rbST) on milk yield, milk composition (fat and protein), milk somatic cell count, and body condition score (BCS) among dairy cattle in a large commercial herd. Regulatory approved 500-mg zinc sesame oil base rbST (ZSO-rbST; Elanco Animal Health, Greenfield, IN) and vitamin E lecithin base rbST (VEL-rbST; LG Life Sciences, Seoul, South Korea) formulations were administered per the manufacturers' recommendations every 14 d over 17 injection cycles starting at 57 to 70 d of lactation (90 cows per rbST group). Control cows (n = 60) received no rbST. Somatotropin-treated animals (VEL-rbST and ZSO-rbST combined) had increased average milk yield and protein percentage and lower average BCS compared with control cows. For primiparous cows, average milk yield was 37.75 kg/d with the ZSO-rbST treatment and 35.72 kg/d with the VEL-rbST treatment. For multiparous cows, average milk yield was 40.13 kg/d with the ZSO-rbST treatment and 38.81 kg/d with the VEL-rbST treatment. There were no differences in milk fat percentage between VEL-rbST and ZSO-rbST treatments, but milk protein content was greater with VEL-rbST treatment than with ZSO-rbST treatment. Nonetheless, cows treated with ZSO-rbST yielded more kilograms of fat and protein per day than cows treated with VEL-rbST. No significant differences in BCS were found between both rbST treatment groups. The differential increase in milk yield between cows treated with ZSO-rbST and VEL-rbST was driven by rbST response differences both within the 14-d cycle and throughout the 17 injection cycles. The cows treated with VEL-rbST demonstrated a more variable 14-d milk yield response curve, with more pronounced valleys between injections compared with the ZSO-rbST formulation. In addition, only the ZSO-rbST treatment was effective in modifying the lactation persistency compared with control cows. Compared with the VEL-rbST formulation, the ZSO-rbST formulation yielded more kilograms of milk, fat, and protein with less milk variation throughout the seventeen 14-d lactation cycles for both primiparous and multiparous cows.     

Effect of kappa-casein and beta-lactoglobulin loci on milk production traits and reproductive performance of Holstein cows

The effects of kappa-casein (kappa-CN) and beta-lactoglobulin (beta-LG) loci on milk production traits (milk, fat, protein, and lactose yield, fat, protein, and lactose content) and reproductive performance (gestation length, calving interval, age at first and second calving, number of services per conception) was estimated for 278 Holstein cows in the first 2 lactations. Genotypes of kappa-CN and beta-LG were determined by alkaline and acidic polyacrylamide gel electrophoresis. Milk production was recorded daily. Single-trait, mixed, linear models were used for the statistical analysis of the data. Results indicated that kappa-CN genotypes affected significantly protein yield and content (genotype AB > genotype AA). A tendency for increased milk and fat yield of animals having AB kappa-CN genotype was also found. Fat content and lactose yield and content were not affected. In the beta-LG system, significant differences were detected for milk yield (AB > AA), fat yield (BB and AB > AA), fat content (BB > AA and AB), and lactose yield (AB > AA). A tendency for higher protein yield was also observed (AB > AA). The beta-LG locus had no significant effect on protein and lactose content. No associations between polymorphisms at the kappa-CN locus and reproductive performance were found. There was a tendency, however, for cows with AB genotype to have older age at first and second calving. In the beta-LG system, cows with AA genotype had significantly shorter gestation length than did those with AB or BB genotype. No differences were detected between beta-LG polymorphisms for the other reproductive traits.     

酶法复合氨基酸锌络合物制备研究

采用木瓜蛋白酶对鱼蛋白进行酶解,以酶解产生的氨基酸与硫酸锌螯合制备复合氨基酸螯合锌。结果表明:酶解的最佳条件是酶用量80mg、底物浓度为1%、酶解时间4h、酶解温度60℃。螯合的最佳条件为氨基酸与硫酸锌的摩尔比为4∶1、pH5.5、反应温度80℃、反应时间40min,所得螯合率达到80.5%。     

Milk protein synthesis as a function of amino acid supply

Most prediction schemes of milk protein secretion overestimate milk protein yield from dairy cows at high protein intakes, thereby overestimating milk protein yield response to protein supplementation. This study was conducted to determine factors contributing to such an overestimation. Using published studies, a database was constructed that was limited to amino acid (AA) infusion studies, as then only the digestible amino acid of dietary origin needed to be estimated, whereas the amount infused was known exactly, thereby reducing the dependence on estimated values. Although milk protein yield was positively related with total energy supply, and both digestible duodenal supply and infused AA, in this database there was no relationship between milk protein yield response above control treatments and the nutrient status of the cows (energy or protein). Total milk protein yield was defined as a function of individual AA supply, using a segmented-linear and a logistic model to obtain estimates of the efficiency of conversion of AA into milk protein. Except for Lys and Met supply, the segmented-linear model yielded lower root mean square error and better correlation, but both models were similar in their reliability. For both models, the estimated efficiency of conversion of AA to milk differed among AA. Estimations of the ideal profile of AA for lactating dairy cows were similar between models, with requirements for Lys and Met in line with 2001 National Research Council recommendations. The major difference is that the segmented-linear model yields a constant efficiency of conversion of an AA until requirements are met, with zero efficiency beyond this point. The logistic model allows for an estimation of the decreasing marginal efficiency of conversion of AA as the supply approaches the requirements. The use of variable efficiency factors should improve our ability to predict protein yield in response to supplemental protein.     

Effect of beta-carotene supplementation on reproductive performance of lactating Holstein cows

Fifty-four lactating Holstein cows were assigned by parity and calving date to a 2 X 3 factorial arrangement of a randomized block design to determine effects of beta-carotene supplementation and ration fiber content on reproduction. Because ration fiber treatments did not differ in their effects on reproductive performance, data for beta-carotene analyses were pooled over the three rations. From 3 to 98 d postpartum, cows were individually fed either 0 or 300 mg supplemental beta-carotene daily by adding it on top of their complete mixed ration. By wk 3 postpartum, concentrations of beta-carotene in blood serum were higher in cows fed supplemental beta-carotene and remained higher throughout the experimental period. Feeding supplemental beta-carotene had no effect on the interval from the time of parturition to uterine involution, ovulation, first observed estrus, or conception. Feeding beta-carotene did not influence incidence of cystic follicles based on palpation, ovarian cyclicity based on blood progesterone patterns, peak progesterone concentrations, or first service conception rate. Cows fed supplemental beta-carotene required fewer treatments for clinical mastitis. Reproductive performance in lactating Holstein cows was not improved by feeding supplemental beta-carotene.     

Effect of peripartum energy concentration on production performance of Holstein cows

Ninety multiparous Holstein cows were used to measure the effect of energy during the prepartum and postpartum periods. During the prepartum period (63 d) half of the cows were fed grass silage ad libitum and a concentrate (16% protein) was offered daily at .25% of BW. The other half of the cows were offered the silage ad libitum but concentrate at .75% of BW. At calving each of the two prepartum groups was subdivided into three subgroups and fed corn silage for ad libitum consumption, 4.5 kg of hay/d and concentrate (20% protein) at .25 or .75% of BW daily, or ad libitum. After 112 d of lactation, all cows were switched to a diet consisting of corn silage fed ad libitum and 1 kg of concentrate (20% protein)/4 kg of milk. Roughage intake was reduced with an increase of concentrate consumption. Body measurements, calf weight, milk yield, feed efficiency, services per conception, and incidence of diseases were not influenced by the prepartum regimen. However, the interval from parturition to conception was 24 d longer for cows on the higher prepartum energy concentration (.75% of BW). None of the cows was able to meet its nutrient requirement in early lactation. Milk yield increased with each increment of concentrate in the postpartum diet. Reproduction and health were not affected by the postpartum regimen.     

Influence of corn silage hybrid type on lactation performance by Holstein dairy cows

The primary objective of this study was to determine lactation performance by dairy cows fed nutridense (ND), dual-purpose (DP), or brown midrib (BM) corn silage hybrids at the same concentration in the diets. A secondary objective was to determine lactation performance by dairy cows fed NutriDense corn silage at a higher concentration in the diet. One hundred twenty-eight Holstein and Holstein × Jersey cows (105 ± 38 d in milk) were stratified by breed and parity and randomly assigned to 16 pens of 8 cows each. Pens were then randomly assigned to 1 of 4 treatments. Three treatment total mixed rations (TMR; DP40, BM40, and ND40) contained 40% of dry matter (DM) from the respective corn silage hybrid and 20% of DM from alfalfa silage. The fourth treatment TMR had ND corn silage as the sole forage at 65% of DM (ND65). A 2-wk covariate adjustment period preceded the treatment period, with all pens receiving a TMR with equal proportions of DP40, BM40, and ND40. Following the covariate period, cows were fed their assigned treatment diets for 11 wk. nutridense corn silage had greater starch and lower neutral detergent fiber (NDF) content than DP or BM, resulting in ND40 having greater energy content (73.2% of total digestible nutrients, TDN) than DP40 or BM40 (71.9 and 71.4% TDN, respectively). Cows fed BM40 had greater milk yield than DP40, whereas ND40 tended to have greater milk yield and had greater protein and lactose yields compared with DP40. No differences in intake, component-corrected milk yields, or feed efficiency were detected between DP40, BM40, and ND40. Milk yield differences may be due to increased starch intake for ND40 and increased digestible NDF intake for BM40 compared with DP40. Intake and milk yield and composition were similar for ND40 compared with BM40, possibly due to counteracting effects of higher starch intake for ND40 and higher digestible NDF intake for BM40. Feeding ND65 reduced intake, and thus milk and component yields, compared with ND40 due to either increased ruminal starch digestibility or increased rumen fill for ND65. Nutridense corn silage was a viable alternative to both DP and BM at 40% of diet DM; however, lactation performance was reduced when nutridense corn silage was fed at 65% of DM.     

Effects of rumen-protected methionine and other essential amino acid supplementation on milk and milk component yields in lactating Holstein cows

Objectives of this study were to investigate the effects of supplementing rumen-protected methionine (RP-Met), threonine (RP-Thr), isoleucine (RP-Ile), and leucine (RP-Leu) individually or jointly to a low-protein diet, on the performance of lactating dairy cows, as well as to determine the effects of these amino acids (AA) on the mammalian target of rapamycin (mTOR) in vivo. Ten lactating Holstein cows were randomly allocated to a repeated 5 × 5 Latin square experiment with five 19-d periods. Treatments were high-protein diet (16% crude protein, positive control; HP), low-protein diet (12% crude protein, negative control; LP), LP plus RP-Met (LPM), LP plus RP-Met and RP-Thr (LPMT), and LP plus RP-Met, RP-Thr, RP-Ile, and RP-Leu (LPMTIL). The dry matter intakes (DMI) of the LP, LPM, and LPMT diets were lower than that of the HP diet, whereas the DMI of the LPMTIL diet was intermediate between the HP diet and the other LP diets. Supplementing RP-Met to the LP diet increased the yields of milk and milk protein, increased the content of milk urea N, and tended to increase milk N efficiency. Co-supplementation of RP-Thr with RP-Met resulted in no further milk production increase. Co-supplementation of all 4 rumen-protected amino acids (RP-AA) increased milk and lactose yields to the level of the HP diet and tended to increase milk protein yield compared with the LPMT diet. We found no significant differences in the contents and yields of milk components between the LPMTIL and HP diets except for a lower milk urea N content in the LPMTIL diet. Venous concentrations of the measured AA were similar across the LP and LP diets supplemented with RP-AA. Relative to levels of the HP diet, LP diets had higher venous concentrations of Met and Gly and tended to have higher Phe concentration and lower concentrations of Val and BCAA. The LPMTIL diet had higher venous concentrations of Arg, Lys, Met, Phe, and Glu, and a lower Val concentration. Phosphorylation status of the measured mTOR components in LPM and LPMT treatments were similar to those in the LP treatment but phosphorylation status of mTOR and eIF4E-binding protein 1 (4eBP1) in LPMTIL treatment were higher. The phosphorylation rates of eukaryotic elongation factor 2 (eEF2) in the 4 LP and LP plus RP-AA diets were higher than that of the HP diet. Overall, results of the present study supported the concept that under the relatively short time of this experiment, supplementing RP-AA, which are believed to stimulate the mTOR signal pathway, can lead to increased milk protein yield. This increase appears to be due to increased DMI, greater mTOR signaling, and greater eEF2 activity.     

Investigating the effect of temporal,geographic, and management factors on US Holstein lactation curve parameters

We fit the Wood's lactation model to an extensive database of test-day milk production records of US Holstein cows to obtain lactation-specific parameter estimates and investigated the effects of temporal, spatial, and management factors on lactation curve parameters and 305-d milk yield. Our approach included 2 steps as follows: (1) individual animal-parity parameter estimation with nonlinear least-squares optimization of the Wood's lactation curve parameters, and (2) mixed-effects model analysis of 8,595,413 sets of parameter estimates from individual lactation curves. Further, we conducted an analysis that included all parities and a separate analysis for first lactation heifers. Results showed that parity had the most significant effect on the scale (parameter a), the rate of decay (parameter c), and the 305-d milk yield. The month of calving had the largest effect on the rate of increase (parameter b) for models fit with data from all lactations. The calving month had the most significant effect on all lactation curve parameters for first lactation models. However, age at first calving, year, and milking frequency accounted for a higher proportion of the variance than month for first lactation 305-d milk yield. All parameter estimates and 305-d milk yield increased as parity increased; parameter a and 305-d milk yield rose, and parameters b and c decreased as year and milking frequency increased. Calving month estimates parameters a, b, c, and 305-d milk yield were the lowest values for September, May, June, and July, respectively. The results also indicated the random effects of herd and cow improved model fit. Lactation curve parameter estimates from the mixed-model analysis of individual lactation curve fits describe well US Holstein lactation curves according to temporal, spatial, and management factors.